1. Field of the Invention
The present invention relates to a Plasma Lighting System (PLS), and particularly, to a PLS which is capable of improving light-transmittance, and a control method thereof.
2. Background of the Invention
In general, a Plasma Lighting System (PLS) refers to a lighting device which can provide a great amount of light even without an electrode by changing inactive gases within a bulb into a plasma state using an electromagnetic wave generated from a high frequency oscillator (i.e., a magnetron) and thus by consecutively emitting light.
The PLS can be used for a long time without a light velocity degradation because of an emission of light based upon a principle for a plasma emission. The PLS can also protect a user's eyesight because of an implementation of a consecutive light spectrum which is the same as that of a natural white color, and provide a comfortable lighting environment by reducing an emission of ultraviolet or infrared rays.
FIG. 1 is a block diagram illustrating a construction of a related art PLS.
As illustrated in FIG. 1, a related art PLS includes a power source unit 1, a rectifying unit 2, a semi-bridge inverter 3, a controlling unit 4, a transforming unit 5, a high voltage generating unit 6, and a magnetron 7.
The power source unit 1 supplies an alternating current (AC) voltage to the PLS for an operation thereof.
The rectifying unit 2 rectifies and smoothes the AC voltage inputted through the power source unit 1 and outputs a direct current (DC) voltage accordingly.
The semi-bridge inverter 3 inverts the DC voltage outputted from the rectifying unit 2 into an AC voltage according to switching control signals and outputs the inverted AC voltage.
An explanation will be made later in detail for an inner construction of the semi-bridge inverter 3.
The controlling unit 4 outputs the switching control signals to alternately switch first and second transistors S1 and S2 of the semi-bridge inverter 3.
The transforming unit 5 transforms the AC voltage outputted from the semi-bridge inverter 3, namely, induces a voltage obtained by transforming the AC voltage based upon a certain winding ratio of a primary coil toward a secondary coil.
The high voltage generating unit 6 generates a high voltage by multiplying the voltage which has been induced to the secondary coil by the transforming unit 5. Here, an explanation will later be made for an inner construction of the high voltage generating unit 6.
The magnetron 7 generates microwaves by receiving the voltage generated by the high voltage generating unit 6 as a driving voltage.
FIG. 2 is a circuit diagram showing the related PLS, and FIG. 3 is a waveform view showing an operation of the related art PLS.
Referring to FIGS. 2 and 3, the controlling unit 4 applies switching control signals S1 and S2 for alternately switching a first transistor S1 and a second transistor S2 respectively to gates G2 and G3 of the first and second transistors S1 and S2. It is thus possible to increase and decrease a resonant voltage and a current according to an on/off period of the switching control signals S1 and S2.
Here, a voltage and a current flowing on a primary coil of the transforming unit 5 are denoted as ‘V1’ and ‘i1’, respectively. On the basis of the voltage V1 and the current i1 flowing on the primary coil, a voltage Vd rectified by the rectifying unit 2 is applied to the first transistor S1, and a negative voltage −Vd of the voltage Vd rectified by the rectifying unit 2 is applied to the second transistor S2.
The current i1 flowing on the primary coil of the transforming unit 5 can be noticed as shown in FIG. 3.
Next, the high voltage generating unit 6 multiplies the voltage induced to the secondary coil by the transforming unit 5 via a capacitor C, diodes D1 and D2 and a resistance R, and applies a high voltage obtained accordingly to the MGT 7.
The MGT 7 then receives the inputted high voltage as a driving voltage and thus generates microwaves.
The microwaves oscillated in the MGT 7 are applied to a bulb via a wave-guide and a resonator. As a result, gases within the bulb are changed into a plasma state due to an electron collision to thus generate light.
It is effective to increase a light-transmittance when operating the PLS using a pulse signal. However, the PLS using the resonant semi-bridge inverter can not be operated using the pulse signal, resulting in degradation of the light-transmittance.